Some construction machines have a counterweight for ensuring the balance of the machine body. These construction machines are generally known to have a configuration in which the counterweight, when mounted on the machine body, is supported by a counterweight support through fastening bolts, the counterweight support being provided in the rear portion of the vehicle body frame. For instance, in a hydraulic shovel, an example of a construction machine, the counterweight support is provided in the rear portion of the vehicle body frame (slewing frame) configuring the base of an upper slewing body, wherein the counterweight is supported by the counterweight support through fastening bolts fastened thereto. In such a construction machine, the counterweight support has a counterweight mounting seat surface that is integrally fixed by adhesion or the like to the rear portion of the vehicle body frame to configure a part of the vehicle body frame and comes into surface-contact with the counterweight, wherein the counterweight mounting seat surface is sometimes machined to ensure a flat surface or to form fastener holes (screw holes) for the fastening bolts by using machine tools.
Incidentally, many of the construction machines are large vehicles, and the larger the vehicle sizes, the more difficult it is to machine the counterweight mounting seat surface after the completion of the assembly of the vehicle body frame, because of the size of the machine tools. Therefore, a counterweight support in which the counterweight mounting seat surface has already been machined beforehand is welded to form the vehicle body frame. In this case, however, the counterweight support might become shifted from a predetermined regular position thereof due to welding stress or the like that occurs upon the assembly of the vehicle body frame, resulting in shifting of the counterweight mounting seat surface and fastener holes from their regular positions. Especially when the reference for positioning is set at the front side of the vehicle body frame or a slewing bearing portion, the counterweight support located on the rear end side of the vehicle body frame is displaced significantly due to the accumulation of welding stress. This makes it difficult to attach the counterweight and generates a gap or level difference between the counterweight and a vehicle body cover or a skirt channel disposed in front of the counterweight, because the counterweight is attached with the counterweight support being displaced, resulting in damaging the appearance.
There have conventionally been known a technique for configuring the counterweight support by using a vertical plate extending from the vehicle body frame, a back plate and a bottom plate adhered respectively to upper and lower end surfaces of the vertical plate, and a pipe member that is capable of sliding vertically between the back plate and the bottom plate and has a counterweight mounting seat surface (counterweight supporting surface) on its upper surface, wherein the pipe member is adhered to a back plate and the bottom plate after the back plate and the bottom plate are adhered to the vertical plate, and a technique for adhering the back plate to the vertical plate extending from the vehicle body frame and thereafter adhering a block having a counterweight mounting seat surface on its upper surface to a cutout portion of the back plate.
Furthermore, there has also been known a technique for forming a boss fitting hole in the rear portion of the vehicle body frame, forming a boss capable of coming into engagement with the boss fitting hole in a front surface of the counterweight, and attaching the counterweight to the vehicle body frame by fastening a bolt passing through the boss, wherein the boss fitting hole is shaped into an oval having the horizontal length greater than the vertical length, and the boss fitting position in the boss fitting hole can be displaced/adjusted by a small amount in the lateral direction.